omc starts missing after extended use

[clafever]

I have an '81 OMC 120 stern drive that starts missing after I have run the boat for a good half hour, less time if fully loaded with passengers. I have tried replacing the coil, which worked the first time this happened a few years ago, but that does not seem to be the issue now, as I have tried replacing the coil again with no luck.

If checking for the problem is too involved I will probably take it to the marina, but it would be nice to have an idea as to what might be wrong.

Thanks in advance for your help.

Chad

 

[full stringer]

Re: omc starts missing after extended use

if you havent recently checked the plugs do that if you haven't replaced em do it. but if you already replaced them double check the gapping. unless you are sure they were gapped correctly. also check there are no burn spots on the plug wires since you mentioned it does it after warming up. only other thing to check for now is the choke if you have one connected make sure its open after warm up. a bad coil will cause your symptoms to sometimes because it gets too hot and puts out erratic voltage

 

[clafever]

Re: omc starts missing after extended use

I recently had the plugs changed and since it was done by the mechanics at my local marina I assume they were gapped correctly. I'll check the wires. I don't think they've been replaced in a while. I replaced the coil last year. Is it possible I got a bad coil? Can it be tested to see if its good?

Thanks for the info.

 

[Bondo]

Re: omc starts missing after extended use

Ayuh,... I'd sooner think it's a fuel delivery issue...
Plugged vent, tank fitting, fuel filter, etc...

 

[superbenk]

Re: omc starts missing after extended use

Anti-siphon valve fixed a similar problem for me (it's on the tank at the gas pickup).

 

[TiredoleBoy]

Re: omc starts missing after extended use

First off what s your definition of missing? Sometimes it means differently than it does to others.
But if it is what I am thinking,
warm engine, miss ( skipping beat to a plug or two), Water spray bottle and hit the wires with it while running. See if it misses while doing this. Sometimes when an engine warms, the wires will expand causing a spark to jump through a minute crack. It may not e visible, but it is there. '81 does it still have points? A condenser when hot will do this as well.